System and method for electronic actuation of axle driving apparatus

ABSTRACT

A system and method for electronically controlling the displacement of hydraulic pumps, transmissions or transaxles. A moveable swash plate is cooperable with a rotatable hydraulic pump for controlling the output thereof, and a rotatable trunnion arm is coupled to the moveable swash plate. A pair of switches may be mounted in separate locations to detect the position of a control arm used to rotate the trunnion arm. The control arm may be connected to an electronic actuation drive used to electronically control the rotatable control arm.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is a continuation of U.S. application Ser. No.11/278,186 filed on Mar. 31, 2006 now U.S. Pat. No. 7,165,398, which isa continuation of U.S. application Ser. No. 10/924,526 filed Aug. 24,2004, now U.S. Pat. No. 7,024,853, which is a continuation of U.S.application Ser. No. 10/290,620 filed Nov. 7, 2002, now U.S. Pat. No.6,955,046. These prior applications are incorporated herein by referencein their entirety.

BACKGROUND OF THE INVENTION

This invention relates generally to hydraulic pumps and axle drivingapparatus and, more particularly, to a system for electric actuation ofsuch devices, including electronic circuitry to automatically drive theaxle driving apparatus to a neutral position.

Hydraulic pumps, transaxles, hydrostatic transmission assemblies(“HSTs”) and integrated hydrostatic transaxles (“IHTs”) are known in theart. Generally, these devices include an end cap or a center section onwhich is mounted a rotating hydraulic pump and, in some applications, arotating hydraulic motor. The hydraulic pump and the hydraulic motoreach carry a plurality of reciprocating pistons, which are in fluidcommunication through hydraulic porting formed in the center section orthrough hoses to a separate hydraulic motor. Rotation of the hydraulicpump against a moveable swash plate creates an axial motion of the pumppistons that forces an operating oil through the hydraulic porting orhoses to the hydraulic motor to move the motor pistons. The axial motionof the motor pistons causes the hydraulic motor to rotate as the motorpistons bear against a thrust bearing. In this manner, the rotation ofthe hydraulic motor may be used to drive the vehicle axles of a ridinglawn mower, small tractor and the like. Separate hydraulic motors suchas geroller, radial piston, and gerotor are also known and similarlyfunction to drive a motor output shaft or one or more axles.

To adjust the speed and direction of rotation of the hydraulic motorand, accordingly, the speed and direction of rotation of the vehicleaxles, the position of the swash plate with respect to the hydraulicpump pistons may be changed. The orientation with which the swash plateaddresses the hydraulic pump pistons can be changed to control whetherthe hydraulic motor rotates in the forward direction or in the reversedirection. Additionally, the angle at which the swash plate addressesthe hydraulic pump pistons can be changed to increase or decrease theamount of operating oil that is forced from the hydraulic pump to thehydraulic motor to change the speed at which the hydraulic motorrotates.

For use in changing the position of the moveable swash plate, it isknown to include a trunnion arm that is coupled to the swash plate. Aspeed change lever or a speed change pedal is, in turn, coupled to thetrunnion arm through a series of rods and levers or other driving link.In this manner, movement of the speed change lever/pedal results inmovement of the trunnion arm to change the position of the swash plateto thereby control the speed and direction of the vehicle. Examples ofsuch mechanisms for adjusting the speed of a vehicle may be seen in U.S.Pat. Nos. 6,122,996 and 5,819,537, which are incorporated herein byreference in their entirety. While these mechanisms for adjusting thespeed of a vehicle have worked for their intended purpose, they requireadditional linkage, which limits the flexibility and ease of transaxleinstallation, and are more difficult for operators to control because ofthe control moments associated with the additional linkage.

For placing the swash plate in a position that neither affects the speednor the direction of rotation of the hydraulic motor, i.e., the neutralposition, some hydraulic pumps or hydraulic transaxles provide a returnto neutral mechanism that is normally implemented as an integral part ofthe vehicle linkage. While these return to neutral mechanisms work fortheir intended purpose, they do suffer disadvantages. For example, theseknown return to neutral mechanisms require complex, costly linkages thatrequire substantial assembly time. These known mechanisms also fail toallow for flexibility with respect to the type and orientation ofdriving linkages that may be used in connection with the hydraulic pump.

SUMMARY OF THE INVENTION

To overcome these disadvantages, the present invention is realized in asystem and method for electrically controlling the displacement ofhydraulic pumps, IHTs or HSTs. Each of these devices includes a variablehydraulic pump mounted within the casing that is in fluid communicationwith a rotatable hydraulic motor, which may also be included within thesame casing as the motor or may be located in a separate casing, and amoveable swash plate cooperable with the rotatable hydraulic pump forcontrolling the speed and direction of rotation of the rotatablehydraulic motor. The rotation of the hydraulic motor is used to drive anoutput shaft which may consist of one or more axle shafts.

For controlling the positioning of the swash plate, the transaxle alsoincludes a rotatable trunnion arm coupled to the moveable swash plate56. The rotatable trunnion arm is also coupled to a control arm. Thecontrol arm is further connected to an electronic actuation drive, whichis mounted either internally or externally with respect to the casing,and is used to control the rotation of the control arm and swash plate.The orientation of the swash plate may be changed to control the speedand direction of rotation of the hydraulic motor.

In an alternative embodiment of the present invention, the drive will beinterlocked with circuitry to automatically return the swash plate to aneutral position under certain predefined conditions. A circuit willalso be described to prevent re-activation of the electric drive untilthe control handle is returned to the neutral position.

The drive will be described in the context of a linear actuator,however, in a further embodiment, a motor driving a worm gear will bedescribed. In an additional embodiment, a motor driving a spur gearreduction configuration will be described.

A better understanding of the objects, advantages, features, propertiesand relationships of the invention will be obtained from the followingdetailed description and accompanying drawings which set forth anillustrative embodiment and which are indicative of the various ways inwhich the principles of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference may be had to apreferred embodiment shown in the following drawings in which:

FIG. 1 is a plan view of a tractor with a simplified representation ofan Integrated Hydrostatic Transmission and other components foroperating the tractor;

FIG. 2 is a close up view of the IHT shown in FIG. 1 without any wiring;

FIG. 3 is an electrical schematic for a drive system using a linearactuator;

FIG. 4 is an electrical schematic illustrating an exemplary circuit forreturning the drive system to a neutral state when a brake is engaged;

FIG. 5 is an electrical schematic illustrating an exemplary circuit fora electronic actuation drive system using Hall Effect sensors toestablish the position of an electric drive;

FIG. 6 is an electrical schematic illustrating an exemplary circuit foran alternative embodiment of the circuit shown in FIG. 5 usingpotentiometers to establish the position of an electric drive;

FIG. 7 is a side view of the IHT shown in FIG. 2 with the side portionof the housing removed and with the actuator located inside the housing;

FIG. 8 is a close up view of an alternative embodiment of the IHT shownin FIG. 2 including a worm gear as part of the actuator mechanism;

FIG. 9 is a close up view of an alternative embodiment of the IHT shownin FIG. 2 including a spur gear configuration as part of the actuatormechanism;

FIG. 10 is a front view of the IHT shown in FIG. 9.

FIG. 11 is a flow chart illustrating an exemplary method of operationfor the drive system circuitry shown in FIGS. 5 and 6.

DETAILED DESCRIPTION OF THE DRAWINGS

Turning now to the figures, wherein like reference numeral refer to likeelements, there is illustrated an electronic actuation drive 10 (“EAD”)for electrically controlling the displacement of a hydraulic pump. TheEAD 10 operates in combination with the general principle of an inputshaft driving a hydraulic pump, which, through the action of itspistons, pushes oil to a hydraulic motor to cause the rotation of amotor shaft. The rotation of the motor shaft may directly drive a wheelor may be transferred through a gearing system or the like to drive oneor more axle shafts 70. All that is required for this invention to beoperative is a variable hydraulic pump. As shown in FIGS. 1, 2 and 7 andin order to simplify the explanation of the workings of this invention,it will be explained in the context of an IHT.

For adjusting the amount of oil that is pushed from the hydraulic pump60 to the hydraulic motor, the hydraulic pump, HST or IHT includes amoveable swash plate 56 against which the pump pistons travel. As willbe understood by those of ordinary skill in the art, the swash plate 56may be moved to a variety of positions to vary the stroke of the pumppistons and the direction of rotation of the hydraulic motor. As thestroke of the pump pistons is varied, the volume of the hydraulic fluidpumped into the hydraulic porting of the center section 62 will vary.Since the speed of rotation of the hydraulic motor is dependent upon theamount of hydraulic fluid pumped into the motor by the hydraulic pump60, and the direction of rotation of the hydraulic motor is dependentupon the positioning of the swash plate 56, the swash plate 56 is seento control the speed and direction of rotation of the hydraulic motorand, accordingly, the speed and direction of rotation of axle shafts 70.

For moving the swash plate 56, the swash plate 56 is connected to amoveable trunnion arm that is rotatably supported in the casing of theHST or IHT. As will be appreciated by those with skill in the art,rotation of the trunnion arm changes the angular orientation of theswash plate 56 with respect to the pump pistons. In addition, a controlarm 40 is coupled to the trunnion arm for rotating the trunnion arm. Itshould be appreciated that the control arm 40, the trunnion arm and theswash plate 56 each cooperate with one another so that movement of oneof these elements will lead to a corresponding movement by the otherelements.

To rotate the control arm 40 and, accordingly, move the swash plate 56,the EAD 10 is coupled to the control arm 40. The EAD 10 may also beconnected to a worm gear, a spur gear or other similar means capable ofcontrolling rotation of the control arm 40. A control handle 14, whichmay be a throttle, a lever, a pedal or similar means for controlling themovement of a vehicle, may be provided on a vehicle, whereby a signalrepresentative of the movement of the control handle 14 is provided tothe EAD 10 to cause the rotation of the control arm 40, the trunnion armand the swash plate 56. The wiring to connect the various components ispreferably located in a wiring harness 50.

For electrically rotating the control arm 40, illustrated in FIG. 3, asource of voltage, in this case a battery 11, is directed through aswitch 12 to an electric drive 16. The electric drive 16 will beattached to the control arm 40 of a swash plate 56 associated with ahydraulic pump, either in a stand-alone unit or as part of an HST orIHT. In this embodiment the electric drive 16 is shown as a linearactuator, but it should be understood by those with skill in the artthat the linear actuator may be replaced with a worm gear, spur gearingor similar means, as discussed in more detail below.

When an operator moves the control handle 14 in one direction, driveactuator switch 12 generates a voltage signal representative of themotion that is then provided to the drive 16. When handle 14 is returnedto a neutral position, signal generation by the switch 12 ceases. Inthis manner, as will be described hereinafter, the vehicle will becaused to drive at the same speed until the handle is moved in theopposite direction to slow the vehicle down or to drive the vehicle inthe opposite direction. While this fundamental circuitry demonstratesthe principles of control. provisions may also be made for braking andstopping.

For controlling the operation of the drive 16 when the brake isactivated, an exemplary brake circuit shown in FIG. 4 may be provided.In the illustrated example, when the vehicle brake is engaged, brakeswitch 18 will be activated. Activation of the brake switch 18 will, inturn, generate a voltage signal that is provided to forward sense switch20 and reverse sense switch 22. The primary function of forward senseswitch 20 and reverse sense switch 22 is to indicate whether the controlarm 40 is physically in a forward or reverse vehicle driving position,which allows the drive 16 to return the control arm 40 to the neutralposition, as described in greater detail below. Forward sense switch 20and reverse sense switch 22 are preferably associated with the HST/IHTcontrol arm 40 as shown in FIGS. 1 and 2, but it should be appreciatedthat they may also be attached to any linkage associated with thecontrol arm 40, such as the linkage attaching drive 16 to control arm 40or the swash plate 56 inside the housing for the pump 60. Switches 20,22 may also be located inside or outside of the housing.

If the HST/IHT control arm 40 has been moved into a position that wouldcause the vehicle to move forward, forward sense switch 20 will beclosed. Once the brake is engaged, brake switch 18 will be activated andthe voltage signal generated by the brake switch 18 will be supplied toactuator 16 through switch 20. Since the polarity of the voltage signalthat is supplied through the activated brake switch 18 is in theopposite direction of the respective switch 20, 22 that is activated,the voltage signal directed through brake switch 18 will always drivethe control arm 40 toward the neutral position, i.e., closing of theforward sense switch 20 ultimately provides a voltage signal causing theactuator 16 to drive the control arm 40 toward a reverse position andclosing of the reverse sense switch 22 ultimately provides a voltagesignal causing the actuator 16 to drive the control arm 40 toward theforward position. Once the control arm 40 reaches the neutral position,switches 20 and 22 will be open and the actuator 16 will no longer beenergized or activated by the voltage signal provided via the brakeswitch.

While the embodiments of the present invention that are described inFIGS. 3 and 4 provide a means of electronically positioning the controlarm 40 of a hydraulic pump, IHT or HST, and returning the control arm 40to the neutral position when the brake is activated, it may also bedesirable to provide for electronically positioning the control arm 40in response to predefined conditions that may arise during normaloperation of lawn and garden vehicles, such as lawn and garden tractorsand utility vehicles.

In the embodiment shown in FIG. 4, if control handle 14 is positioned tomove the vehicle in either a forward or reverse direction and the brakeis then activated, the actuator 16 may be used to drive the control arm40 toward the neutral position. However, if the brake is subsequentlyreleased and control handle 14 remains in the forward position, thenactuator 16 may again cause the vehicle to drive forward. In a furtherexample and as shown in FIGS. 3 and 4, if the ignition of the vehicle isturned off while the actuator 16 is in a forward position and theignition is subsequently turned on again. IHT/HST 38 may immediately tryto drive the vehicle in the direction corresponding to the position inwhich the control handle 14 was last set.

For positioning the control arm 40 in response to predefined operatingconditions, an electronic actuation drive 10 may be provided, which iscapable of providing one or more of the following functions: (1) returnthe control arm 40 to neutral automatically when the engine is turnedoff; (2) return the control arm 40 to neutral automatically when thebrake is activated; (3) require the control handle 14 to be returned tothe neutral position prior to re-activating the drive voltage to theactuator 16; (4) disconnect the voltage signal to any control or drivecomponents when the control arm 40 is in the neutral position and thekey to the vehicle is in the off position so as to prevent the battery11 from being drained; (5) drive the control arm 40 to match theorientation of the control handle 14 by comparing the output voltagesignals associated with the control handle 14 and the control arm 40,and then moving the control arm 40 to match the position of the controlhandle 14; or (6) provide hysteresis in connection with the comparisonelectronics to prevent oscillation or dither of the actuator between theforward and reverse drive modes.

More particularly, FIGS. 5 and 6 show two variations of the electronicactuation drive or EAD 10, which are nearly identical, except that theHall Effect sensors 30 and 32 in FIG. 5 are replaced with variablepotentiometers 130 and 132, respectively, in FIG. 6. All othercomponents in FIG. 6 share the same numbering as those in FIG. 5 and arefunctionally identical to the components in FIG. 5. While thepotentiometers 130 and 132 can provide a voltage output signal similarto that of the Hall Effect sensors 30 and 32, the latter are moredesirable because they are less sensitive to environmental conditionssuch as moisture and debris.

Engine Off Function.

The EAD circuits shown in FIGS. 5 and 6 may drive actuator 16 to theneutral position when the engine is off regardless of the position ofthe control arm 40. For example, when ignition switch 28, which may alsobe a relay or a combination of more than one switch or relay, is in theoff position, voltage signals are directed through contacts 26 a andcontacts 26 b of relay 26. These voltage signals are then connected toswitches 20 and 22. If either forward sense switch 20 or reverse senseswitch 22 is closed, indicating the control arm 40 is in a forward orreverse position, respectively, then a voltage signal will be suppliedto actuator 16. In this configuration, forward sense switch 20 isdesignated as the forward position sensor and, when closed, allows avoltage signal to drive actuator 16 in the reverse direction so as tomove the control arm 40 and the swash plate 56 toward the neutralposition.

Once the control arm 40 and the swash plate 56 are in the neutralposition, switch 20 opens and a voltage signal is no longer supplied tothe actuator 16. Conversely, when reverse sense switch 22 is closed, avoltage signal causes the actuator 16 to drive the control arm 40 towardthe neutral position until switch 22 opens and a voltage signal is nolonger supplied to the actuator 16. It should be appreciated that whenswitches 20 and 22 are both open, the control arm 40 will have beenreturned to the neutral position; therefore, a voltage signal is nolonger supplied to the actuator 16. Furthermore, when the ignitionswitch 28 is in the off position and the control arm 40 is in neutral,no voltage signal is supplied to any control or drive components, whichfunctions to prevent the battery from being drained.

By way of further example, if the ignition switch 28 is in the middle oroperating position, a voltage signal is supplied to Hall Effect sensors30 and 32, comparator 34, and, if control handle 14 is in the center orneutral position and the brake is not activated, to relay 26. Once relay26 is activated, a voltage signal will be directed through contacts 26c, which will provide an additional voltage path to maintain relay 26 inan activated condition. Therefore, relay 26 will remain in aself-holding state until the brake pedal is depressed or until theignition switch 28 is turned to the off position. Relay 26 also providesa voltage signal to contacts 42 a of forward actuation relay 42 andcontacts 44 b of reverse actuation relay 44. Further, control handleneutral switch 36 is coupled to the control handle 14 and will only beclosed when the control handle 14 is in the neutral position. Thus,before a voltage signal may be supplied to self-holding relay 26, thecontrol handle 14 must be in the neutral position (thereby closingswitch 36), the control arm 40 must be in the neutral position (therebyclosing contacts 46 c of neutral sense switch 46), and the brake must bereleased (thereby deactivating brake switch 24).

To prevent the engine from being started when the control arm 40 is notin the neutral position, contacts 46 a of switch 46 may be included aspart of the engine start circuit. Hence, even if another portion of theactuator circuitry allows the engine to be started with the control arm40 in a forward or reverse position due to a system failure, such as adisconnected wire or failed switch, the engine start circuit will stillprevent the engine from being started.

Comparison of Control Handle to Control Arm Positions.

For enabling the EAD 10 to synchronize the output positions of thecontrol handle 14 and the control arm 40 by comparing the outputvoltages associated therewith, Hall effect sensors 30 and 32 areprovided. Hall effect sensors 30 and 32 are linear sensors and in thepreferred embodiment of the present invention they are rotational linearsensors. The Hall Effect sensors 30 and 32 are attached to the rotatingcontrol handle 14 and the rotating control arm 40 and have a constantvoltage output signal proportional to the rotational position of amagnet with respect to the Hall Effect sensor. Other types of HallEffect linear sensors may be attached to other portions of the controland actuation linkage (not shown). The range of rotation is preferably−20 degrees from neutral to +20 degrees from neutral. As the rotation ofthe Hall Effect sensor 30 changes from the −20 degree position to the+20 degree position, an increasing output voltage signal is generated byHall Effect sensor 30 and directed to comparator 34 via wire 31. HallEffect sensor 32 also generates a similar output voltage signal, whichis directed to comparator 34 via wire 33.

For comparing the output voltage signal from Hall Effect sensors 30 and32 and for rotating the control arm 40 until it is synchronized with thecontrol handle 14, comparator 34 is provided. If the output voltagesignal from sensor 30 is at a higher level than the output voltagesignal from sensor 32, then the comparator 34 will send a voltage signalVF to activate relay 42, which then applies a voltage signal to actuator16 in a polarity that drives the control arm 40 in the forwarddirection. As the control arm 40 rotates, rotating the Hall Effectsensor 32 with it, the voltage signal from Hall Effect sensor 32increases until it reaches the level of the voltage signal from HallEffect sensor 30, at which time the comparator 34 turns voltage signalVF off, deactivating relay 42. If the voltage from sensor 30 is lowerthan the voltage signal from sensor 32, then the comparator 34 will senda voltage signal V_(R) to activate relay 44 and the actuator 16 willdrive the control arm 40 in the reverse direction until the voltagesignal level from sensor 32 matches that of sensor 30 and voltage signalV_(R) is turned off.

As comparator circuits are well known to those of ordinary skill in theart, it should be appreciated that comparator 34 may also consist of apair of operational amplifiers, a logic circuit, or a variety of othercircuit configurations designed to compare two voltage signals. Further,while the drive voltage signals are shown as being connected through avariety of switches and relays, it should be understood that suchswitches and relays may be replaced with other electrical componentsoffering similar functions. The relays 26, 42, and 44 and comparator 34are preferably located in control module 52, which is preferably locatedin a position away from the HST/IHT and the vehicle engine.

Hysteresis in Comparator.

To prevent the continuous oscillation of the actuator 16 between theforward and reverse directions, comparator 34 may include a circuit thatadds hysteresis to the voltage signals from sensors 30 and 32. Thehysteresis will be selected based on the operating conditions of aparticular vehicle and will cause comparator 34 to activate relays 42and 44 only if control handle 14 is moved. Adding hysteresis tocomparator circuits is also known to those with ordinary skill in theart and has been described in various technical magazines and books.

Brake Activation.

The circuits shown in FIGS. 5 and 6 are also capable of driving thecontrol arm 40 to the neutral position when the brake is activated. Forexample, assuming the ignition switch 28 is in the center or on positionand the control handle 14 is in the neutral position, the relay 26 willbe activated. After the relay 26 is activated and if the control handle14 is moved in a forward or reverse direction, the comparator will causethe actuator 16 to rotate the control arm 40 accordingly so that thevehicle begins moving in the selected direction. At this time, if thebrake is activated, brake switch 24 will switch opposite to the positionshown in FIGS. 5 and 6. When contacts 24 d assume the open position,switch relay 26 will become deactivated, which removes the drive voltagesignal from relays 42 and 44. When contacts 24 a assume the openposition, the voltage signal may also be disconnected from relays 42 and44. Contacts 24 b provide a voltage signal to forward sense switch 20and reverse sense switch 22, while removing a voltage signal fromcontacts 42 b and 44 a. As noted above, if the operator has positionedthe control handle 14 to cause the vehicle to be in motion, the neutralswitch 46 located on the control arm 40 will be switched to the positionopposite that shown in FIGS. 5 and 6. Therefore, when the brake switch24 is activated a voltage signal will be directed through contacts 24 cto contacts 46 b and then also to switches 20 and 22. Since the vehicleis in motion, either forward sense switch 20 or reverse sense switch 22will be closed, and the voltage signal applied to the respectiveswitches 20, 22 will then be connected to the actuator 16. As a resultof receiving a voltage signal via the closure of switch 20 or 22,actuator 16 will drive the control arm 40 toward the neutral positionuntil neutral is reached and switches 46, 20 and 22 are returned to thestate shown in FIGS. 5 and 6, at which time actuator 16 will stopdriving the control arm 40. As previously noted, prior to reactivatingthe self-holding relay 26, the HST/IHT 38 must have achieved the neutralposition (thereby closing switch 46 c), the control handle 14 will needto be returned to the neutral position (thereby closing switch 36) andthe brake will need to be released (thereby deactivating brake switch24). Once the self-holding relay 26 is reactivated, the EAD 10 willagain be able to supply voltage signals to actuator 16.

FIG. 7 illustrates a further embodiment of the present invention whereinthe actuator mechanism 16 is mounted internally with respect to the IHT38. The side housing 54 was removed in FIG. 7 to expose theconfiguration of the internal components, while leaving Hall Effectsensor 32 in place. In the illustrated embodiment, Hall Effect sensor 32is mounted external to side housing 54 and extends through the sidehousing to mate with swash plate 56 or control arm 140. FIG. 7 alsoillustrates the internal details of other components in housing 55. Aninput shaft 58 drives pump 60 mounted on center section 62. In atransmission configuration, a motor (not shown) is driven throughporting within center section 62. The motor is connected to a motorshaft 63 that drives the motor shaft gear 64, which then drives otherelements of the gear train 66. The gear train 66 may drive a single axleshaft or may be further comprised of a differential 68, which is capableof driving two or more axle shafts 70.

As exemplified in FIG. 11, an electronic actuation drive 10 is providedfor detecting predefined conditions and electronically controlling thepositioning of the control arm 40 and the swash plate 56 in response tothose predefined conditions. For example, in its “start” position, theEAD 10 will initially detect whether the swash plate 56 is in neutral.If the swash plate 56 is not in neutral, the EAD 10 will drive the swashplate 56 back to the neutral position; the operator may not be able tostart the engine, unless the swash plate 56 is in the neutral position.If the swash plate 56 is in neutral, the operator may be permitted tostart the engine. It should also be appreciated by those with skill inthe art that as an added protection against starting a vehicle that mayalready be in the forward or reverse drive positions, the EAD 10 mayalso require the control handle 14 to be in the neutral position priorto allowing the operator to start the vehicle.

When the engine is started, the EAD 10 will then determine whether thevehicle is in operation mode, i.e., whether the control handle 14 is inneutral. When the control handle 14 is not initially in the neutralposition, the operator is unable to move the vehicle in a forward orreverse direction. The EAD 10 will not activate the self-holding relay26 until the EAD 10 determines that the swash plate 56 and controlhandle 14 are in neutral and the engine is on.

After the self-holding relay 26 becomes activated, the operator mayactuate the EAD 10 in the forward or reverse direction by shifting thecontrol handle 14 to the desired position. In addition, once the selfholding relay is activated, the EAD 10 may recursively test for whetherthe brake has been activated, the engine has been turned-off, and thecontrol handle 14 has been placed in the neutral position.

If the brake is activated, the EAD 10 may function to detect whether theswash plate 56 is in neutral. If the swash plate 56 is not in neutral,the EAD 10 may then drive the swash plate 56 back to the neutralposition. Once the swash plate 56 is in the neutral position, the EAD 10may again test for whether the vehicle is in operation mode, asdescribed above. Therefore, once the brake has been activated, the EAD10 may require the control handle 14 to be returned to the neutralposition before re-establishing operator control over the EAD 10. Aslong as the brake is not activated and the engine is still running, thevehicle should continue to respond to movements of the control handle14.

If the brake is not activated, the EAD 10 may then determine whether theengine has been turned-off. If the engine has been turned-off, the EAD10 may detect whether the swash plate 56 is in neutral. If the swashplate 56 is not in neutral, the EAD 10 may drive the swash plate 56 backto the neutral position. After the swash plate 56 is in the neutralposition, the EAD 10 will be in a power-off state and no voltage will beapplied to any electronics until the next time the engine is started.

If the engine has not been turned-off, the EAD 10 may detect whether thecontrol handle is in the neutral position. If the control handle 14 isnot in the neutral position, the engine is still running and the brakehas not been activated, then the EAD 10 may continue to test for thoseconditions. If the control handle 14 is in the neutral position, theswash plate 56 will be driven to the neutral position. It should beappreciated that the operator may periodically return control handle 14to neutral for various operational reasons. When the control handle 14is in neutral and the vehicle has stopped, the operator may elect toeither move the control handle 14 from the neutral position and drivethe vehicle forward or backward, or the operator may decide to turn thevehicle engine off. If the engine is turned-off, the EAD 10 will be in apower-off state and no voltage will be applied to any electronics untilthe next time the engine is started.

While the preferred embodiment of the present invention includes alinear actuator 16, it should be understood that the linear actuator 16may be replaced with other means which produce a similar result. Forexample, as shown in FIG. 8, the linear actuator may be replaced with aworm gear drive 216, which is drivingly associated with an appropriatelyconfigured control arm 240.

In addition, as shown in FIGS. 9 and 10, the linear actuator may also bereplaced with a spur gear reduction actuator 316. This configuration mayconsist of a suitable enclosure 320, such as a housing, that may then beenclosed with a cover 328. This enclosure may also be configured toinhibit entry of contaminants, such as dirt and moisture, by use ofappropriate seals. The actuator 16 may be further comprised of one ormore gear reductions 322 that are drivingly coupled with control arm340. Mounting of a drive motor 318 to enclosure 320 may be achievedthrough a variety of methods currently known in the art, such as nutplates 324 and bolts 326.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangement disclosed is meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any equivalents thereof. Forexample, the method described with respect to electronic actuation of anaxle driving apparatus can be performed in hardware or software withoutdeparting from the spirit of the invention. Furthermore, the order ofall steps disclosed in the figures and discussed above has been providedfor exemplary purposes only. Therefore, it should be understood by thosewith skill in the art that these steps may be rearranged and alteredwithout departing from the spirit of the present invention.

1. A system for controlling the orientation of a swash plate, the systemcomprising: an operator actuated control; an electric actuator incontrolled communication with the operator actuated control and operableto move the swash plate; a first control device in communication withthe operator actuated control; and a second control device in controlledcommunication with the first control device and the operator actuatedcontrol, the second control device having an activated state, whichallows transmission of position signals from the operator actuatedcontrol to the electric actuator to effectuate movement of the swashplate, and a deactivated state, which prevents transmission of positionsignals from the operator actuated control to the electric actuator,wherein the second control device, once activated, maintains theactivated state until any one of a plurality of conditions is met; andwherein when the second control device is in the deactivated state, thefirst control device, upon placement of the operator actuated control ina position that equates to a neutral swash plate position, transmits anactivation signal to the second control device, activating the secondcontrol device.
 2. The system of claim 1, wherein the first controldevice is a electronic switch.
 3. The system of claim 1, wherein thesecond control device is a relay.
 4. The system of claim 1, furthercomprising a brake switch, wherein actuation of the brake switch causesthe second control device to be deactivated, thereby preventingtransmission of signals from the operator actuated control to theelectric actuator.
 5. The system of claim 4, further comprising a thirdcontrol device, wherein upon actuation of the brake switch, the thirdcontrol device transmits a return signal to the electric actuator tocause the electric actuator to move the swash plate to the neutralposition.
 6. The system of claim 5, wherein the third control deviceceases transmission of the return signal when the swash plate reachesthe neutral position.
 7. The system of claim 5, further comprising afourth control device for determining the direction in which theelectric actuator needs to move to place the swash plate in the neutralposition.
 8. The system of claim 7, wherein the fourth control devicecomprises a plurality of switches.
 9. A mechanism for remotelycontrolling a swash plate, the mechanism comprising: an electricallypowered actuator for orienting the swash plate in a neutral position anda plurality of non-neutral positions; a control circuit in communicationwith the electrically powered actuator and enabled by placing anoperator control in a position that equates to the neutral position ofthe swash plate; a return to neutral circuit in communication with theelectrically powered actuator; and a brake switch in communication withthe control circuit and the return to neutral circuit; wherein actuationof the brake switch disables the control circuit while permitting thereturn to neutral circuit to send drive signals to the electricallypowered actuator to move the swash plate to the neutral position. 10.The mechanism of claim 9, further comprising a direction sensing devicefor determining in which direction the electric actuator needs to moveto return the swash plate to the neutral position.
 11. The mechanism ofclaim 10, wherein the direction sensing device comprises a plurality ofswitches.
 12. The mechanism of claim 11, wherein the return to neutralcircuit ceases sending drive signals to the electric actuator when theelectric actuator reaches the neutral position.
 13. A vehicle propelledby a hydrostatic transmission, the vehicle comprising: a mechanism forcontrolling the displacement of the hydrostatic transmission, themechanism having a neutral position and a plurality of non-neutralpositions; an electrical actuator for positioning the mechanism; anoperator control in communication with the electrical actuator andhaving a neutral position and a plurality of non-neutral positions; anda first electrical circuit in communication with the operator controland the electrical actuator, and having a disabled condition whereinsignals from the operator control are prevented from reaching theelectrical actuator and an enabled condition wherein signals from theoperator control are transmitted to the electrical actuator; wherein thefirst electrical circuit is enabled by placing the operator control inthe neutral position.
 14. The vehicle of claim 13, further comprising abrake switch, wherein actuation of the brake switch causes the firstelectrical circuit to be in the disabled condition.
 15. The vehicle ofclaim 14, further comprising a second electrical circuit, whereinactuation of the brake switch allows the second electrical circuit tocause the electric actuator to move the control mechanism to the neutralposition.
 16. The vehicle of claim 15, further comprising a thirdelectrical circuit for determining in which direction the electricactuator needs to move to return the control mechanism to the neutralposition.
 17. The vehicle of claim 16, wherein the third electricalcircuit comprises a pair of switches.
 18. An electrical circuit forenabling the movement of an actuator by an operator control, theelectrical circuit comprising: a first control device having an enabledstate that allows signals to be transmitted from the operator control tothe actuator and a disabled state that does not allow signals to betransmitted from the operator control to the actuator; wherein theoperator control is in communication with the actuator and has a neutralposition and a plurality of non-neutral positions; and wherein theenabled state is attained by placing the operator control in the neutralposition.
 19. The electrical circuit of claim 18, further comprising abrake switch, wherein actuation of the brake switch causes the firstcontrol device to be placed in the disabled state.